1. Field of the Invention
The present invention relates generally to portable testers for measuring the water content of a material using a measurement of the dielectric constant of the material, and more particularly to such a moisture tester which uses lookup tables that are calibrated to match the moisture measurement ranges of several commercial moisture testers and which measurements allows offset calibration adjustments to more closely match individual commercial testers being used.
2. Description of the Prior Art
There have previously been portable grain moisture testers that have been calibrated to absolute grain moisture. One shortcoming of this is when the portable moisture tester measurement is taken in the field and is then compared to a commercial tester measurement at the grain purchase site and the two measurements do not give the same result. Since the farmer""s return for selling his grain is directly correlated to the optimum percent moisture content as measured by the commercial tester, the portable unit needs to match the commercial tester and provide harvesting of the grain at this optimum commercial measurement. Prior art devices failed to overcome this mismatch and provided no way to calibrate the portable tester to several commercial testers instead of calibrating directly to absolute moisture.
Portable grain moisture testers are known and are described in U.S. Pat. Nos. 4,462,250 and 3,739,264. They give no option of selecting a grain moisture curve to match the commercial tester. Each of these units has one fixed moisture curve per grain. While this is a valid approach, it has been revealed that calibrating to several commercial testers, and allowing the user to select the calibration curve results in a more cost effective grain measurement which results in a top price for the grain at the commercial tester site by insuring an optimum moisture measurement with no penalties for drying overly wet grain.
Prior art portable moisture meters as shown in U.S. Pat. No. 5,663,650 teach a method for providing offset adjustments in an attempt too more closely match the commercial testers. These meters offer a single offset for the entire moisture span which eliminates the possibility of adjusting to the commercial tester""s complete moisture span, and only allows the user to add a single calibration offset to the entire moisture curve. This method is acceptable if the user is always working in a narrow window of the total moisture span. However, the lack of multiple offsets over the entire grain moisture span would sometimes cause an adjusted low moisture range to match the elevator but the higher moisture would be further off than if it was with zero offset because low and high moisture offsets are often of opposite polarity.
Also, known prior art portable moisture meters provided compaction of the grain test sample by filling the test cell with grain and compressing it by screwing down the cap over the test cell. This provided a test under differing grain compactions depending on the strength or disposition of the person initiating the test resulting in a lack of complete repeatability of testing. There was no provision for initiating a test under a preset compaction of the grain sample.
In view of the forgoing it will be seen that the prior art portable grain moisture measurement devices failed to provide a repeatable test under a preset constant compaction or pressure, did not calibrate to several commercial moisture testers and did not provide sufficient calibration offset.
The present invention solves the problems associated with prior art portable moisture meters and others by providing a meter which has a means for a farmer to closely match the measurements of various commercial elevator testers for the commodity that he is selling to insure optimum moisture content measurements by the commercial tester. Since most testers calibrations are based on absolute moisture and every manufacture has a different calibration it is very difficult for a moisture tester with one calibration to match a large range of commercial testers on the market. The present device uses multiple calibrations, each commodity to be tested has a different calibration for each of the commercial testers that the farmer may encounter at his particular grain purchase site. This will ensure that the farmer can more closely match the site""s elevator tester measurements for optimum moisture content.
To accomplish this end, the present device use a graphic LCD with a menu driven interface to not only allow the operator to select the commodity to be tested but also to select the commercial tester that his measurements will be compared against.
Before the farmer begins to test the commodity he first turn on the tester. The tester""s LCD will display on the screen some instructions, and also the last commodity that was tested. Next he presses the menu button. The tester now displays a series of menu options the user will then using the arrow keys move the pointer down to select the menu option commercial tester and press the enter key. The tester now displays the list of commercial testers that are calibrated in the tester. Using the arrow keys he moves the pointer to the commercial tester that he wants to compare to and presses enter. Once enter is pressed the selection is stored and the tester returns to the main menu display. The farmer can now either select another menu option or press the cancel button to return to the main screen where the commodity to be tested is displayed. The user can now prepare to test that commodity or use the up down arrows to select a different commodity.
To initiate a test with the tester the user fills the tester with the commodity he wants to measure. Once the test cell is full the tester will display TEST INITIATED and the farmer now has 60 seconds to place the cap on the unit and tighten down the cap. The tester now, by measuring the compaction of the commodity in the cell, determines the correct time to take a test. This is done by having the test start automatically at a predetermined pressure on the grain sample in the cell as determined by a strain gauge located in the cell. The strain gauge signal is compared to a preset level stored in a microprocessor which initiates testing upon detecting the preset level. The pressure on the grain is done by screwing down the cap of the tester. Once the test is initiated the tester will audibly beep and provide an indication on the LCD showing TESTING. At this point the user should stop tightening the cap and the tester is now measuring the commodity to determine the moisture by measuring the dielectric of the commodity and also the temperature. Once it is done the tester uses the dielectric reading to lookup the corresponding moisture value using the calibration curve for the commercial tester selected by the user and then applies any user offset that have been made. The tester then applies the temperature compensation to the resulting moisture value based not only by the temperature of the commodity but also the initial moisture calculated before temperature compensation. Then the tester displays on the screen the current moisture value of the last six tests and the average of them.
If the user is not satisfied that his portable tester matches the commercial tester, he has the option of adjusting the calibration of his tester by pressing a cal button. After the cal button is pressed a menu appears giving him the option to reset or adjust the calibration of the tester. If he selects RESET all the offsets that were in the tester will be set back to factory calibration. A menu will appear to confirm that he wishes to reset the given commodity using the selected commercial tester. If the user wishes to adjust the moisture reading, a new window will appear showing the value of the current moisture tested and also showing the same value for the commercial tester. The user can now use the arrow keys to adjust the reading to the actual reading of the particular commercial tester he is selling his grain to by not just applying an offset but actually changing his tester reading to that of the commercial tester. The tester now shows on the display the amount of adjustment that the user has made as well as the maximum amount that he can adjust. Once the adjustment is made the tester takes the offset value and applies it to the calibration of the commodity only in the moisture range of the current test. The tester does not apply an offset to the whole calibration but only to the point that was just tested. This is important for reason as described above.
From the foregoing it will be seen that one aspect of the present invention is to provide a portable grain moisture meter having a stored memory of commercial tester moisture meter measurement ranges for numerous commercial tester manufacturers which may be used in the portable meter.
Another aspect of the present invention is to provide a portable grain moisture meter having a stored memory of commercial tester moisture meter measurement ranges for numerous commercial tester manufacturers which may be manually changed by the portable meter user to conform a stored measurement to an actual measurement of a particular commercial tester.
Still yet another aspect of the present invention is to provide a portable grain moisture meter having an automatic test initiation of moisture measurement upon a predetermined test cell compaction of grain therein.
These and other aspects of the present invention will be more fully understood upon a review of the following description of the preferred embodiment when considered in conjunction with the drawings.